Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 182312

Area Forecast Discussion
National Weather Service La Crosse WI
612 PM CDT Fri May 18 2018

.SHORT TERM...(This evening through Saturday)
Issued at 313 PM CDT Fri May 18 2018

At 3 PM, east winds on the southern periphery of a Canadian high
pressure system continued to bring dry air into the Upper
Mississippi River Valley. While the radar and some of the meso
models (ARW, NMM, and HRRR) are trying to produce rain, the air
mass below 600 mb remains rather dry, so we have not been seeing
any of this rain reaching the ground. This trend should continue
for the remainder of the afternoon.

For tonight, we will remain in between low pressure systems. One
low pressure system, currently located over the Mid Mississippi
River Valley, will move northeast into the southern Great Lakes.
Meanwhile, a cold front will remain off to our northwest.

On Saturday, a cold front will move southeast through the area.
As low level moisture pools along and north of this front, there
may be enough instability for scattered showers and isolated
storms to develop across southeast Minnesota and in west-central
and north-central Wisconsin.

.LONG TERM...(Saturday night through Friday)
Issued at 313 PM CDT Fri May 18 2018

From Saturday night through Sunday, the models are in general
agreement that the precipitation will be found along and south of
Interstate 94. With limited instability, only expecting periodic
showers with this wave.

From Sunday night into Monday night, the models continue to differ
on the northern extent of showers. Both the GFS and GEM are
further northwest with the upper level short wave, so showers end
up occurring across much of the area. Meanwhile, the NAM and
ECMWF are further southeast with their upper level short wave and
also have the Canadian high a bit further south, so as a result
they have their rain remaining mainly south of Interstate 90.

From Wednesday through Friday, the models are in general agreement
that a short wave trough will slowly move from the Northern Plains
into the Great Lakes. This system will provide a chance of showers
and storms. With weak 0-3 and 0-6 km shear, not anticipating any
severe weather from these storms.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 612 PM CDT Fri May 18 2018

VFR conditions continue this evening, but this is a bit of a
tricky forecast later tonight and into Saturday as weak low
pressure passes just to our east tonight and a cold front lays out
across the region tomorrow. Some mid level clouds from that system
to the east are likely to skirt LSE roughly 06-09Z but at this
time, don`t envision lower stratus in place over northern IL at
this time to work that far west. Meanwhile, RST could deal with
some mid level clouds at times, but light flow and higher dew
points should allow for at least a little light fog overnight. As
the cold front then approaches from the west, it appears that
plentiful lower stratus (already in place to our north over the
Dakotas) will overtake the region, likely developing into more of
a stratocumulus cloud deck with eastward extent. Exact timing of
those clouds is tricky and they could hold off longer than
currently forecast for LSE, but the upshot is that most areas
should end up with MVFR ceilings (maybe briefly IFR at RST)
through the day on Saturday, with actual ceiling heights very
slowly rising into the afternoon. Lighter winds from the
southeast this evening will shift northwest at 10-15 knots behind
the cold front Saturday.




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